The ISO 21702 evaluates the antiviral activity of treated plastic and non-porous products such as water-repellent textiles, paints, metal surfaces, ceramics, etc. Some of the viruses used to test the antiviral ability of the product are the Influenza A virus, Human coronavirus, Feline calicivirus, etc. Additionally, the ISO 21702, in combination with a durability test, offers significant insight into the anti-viral performance of the sample material under environmental conditions.

Test protocol

  1. Conventionally, triplicates of 5 × 5 cm squares are used. These include six square pieces of the test surface and nine squares of the inert control surface. 
  1. 400 µl of the virus is added to each test and control square. After the standardized contact time, liquid media is used to recover the remaining virus.
  1. The viability of the virus on the test and control surfaces is now measured indirectly. This is done by examining the effect of the infection on mammalian host cells.
  1. The remaining virus is then diluted in a ten-fold dilution. It is then subsequently added to cells cultured in 96-well plates. 
  1. The virus is incubated with the cultured cells for a standardized time to allow the progression of infection. 
  1. After incubation, formaldehyde is used to fix the cells. They are then stained using crystal violet to differentiate between virus-infected (white) or uninfected (violet) cells. 
  1. Individual wells are scored as infected or not infected. This information is used to estimate the final R-value for the tested surface.

Also Read: ISO 18184 – Virucidal antimicrobial activity on textiles

Calculating the antiviral activity of a surface

The R-value refers to the decrease in the concentration of the virus on the sample corresponding to a control sample. It is calculated as the difference between the amount of virus remaining on the reference and the test sample (both of which are expressed as base 10 logarithms). 

For the antiviral activity to be established, the sample tested must obtain an R-value of 2 or more. 

R-Value Interpretation
R = 1 equivalent to a 90% reduction of infectious virus relative to the control sample
R = 2 99% reduction
R = 3 a reduction of 99.9%

Viruses degrade and become inactive on any surface over time. This makes it essential for the R-value to be measured correspondingly based on the inert control. 

The R-value gives the information on virus inactivation due to the sample. The viral activity is calculated using the above method due to the potential difference in lab conditions each day and batch variability in the virus stock used. 

Reporting a relative value allows for control over these variations while testing only the result of the antiviral treatment.

Controls

This section describes the various controls used for the ISO 21702 test alongside the sample.

1. Cytotoxicity control

ISO 21702 test evaluates the cytotoxicity toward cells cultured in liquid media under precise lab conditions. This control does not attempt to evaluate the toxicity in a real-world setting. It strengthens the interpretation of the antiviral test. 

Also Read: Top Facts about the JIS L 1902 Test Method

2. Untreated Sample control

Often, many plastics and nonporous substances have been shown to possess inert antiviral activity against many viruses. The inert antiviral activity of the surface and the compound coated on it need to be differentiated. This is done by adding the virus to the untreated surface for the same time as the test sample. After incubation, the collected virus is used to determine the antiviral action of the untreated surface. This acts as an essential control in determining the true antiviral potential of the compound on the surface. 

3. Titration control

If the concentration of the virus were too less, it would symbolize a problem with the virus stock. Hence, the virus is obtained from the viral stock directly and added to the host cells to determine the initial concentration of the virus in the experiment. 

This provides a valuable standard to detect if there was an excellent infectivity titer of the virus for testing the sample. Additionally, it offers information on the highest concentration of virus that labs can recover from the testing. 

Microbe Investigations

Founded in 2012 by a group of ETH researchers in the Institute of Food, Nutrition, and Health at ETH Zürich, Microbe Investigations is a spin-off company of the Swiss Federal Institute of Technology in Zürich. 

The ISO 21702 test duration is two weeks, and we test using the following viruses: SARS CoV-2,  Beta Coronavirus (OC-43) (ATCC VR-1558), Human Coronavirus (229E) (ATCC VR-740), Influenza A (H1N1) (ATCC VR-1469), Influenza A (H3N2) (ATCC VR-1679). The booking process is rapid and straightforward. We will do the ISO 21702 testing at our lab and submit the report on your preferred date. 

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